The acoustical laminate of the present invention has many applications as decorative and functional covering for the walls and ceilings of offices and institutions such as banks, hotel lobbies, schools, hospitals and the like. The laminate structures may also be advantageously used on the ceiling and walls of entertainment areas such as concert halls, theater, nightclubs, etc. They may also be used as inside surface coverings for transportation vehicles such as trains, planes and buses. The laminate structures have further applications in the manufacture of divider screens for office space, acoustical louvers for windows and the like.
While not intended to be so limited, the laminate structures of the present invention will be described in terms of their application to the walls of office spaces. In recent years office architects have turned more and more to the open plan office comprising a large interior area having no interior walls or a minimum of such walls. The open plan office offers a number of advantages over conventional walled offices including improved communication at all levels, improved flexibility (employees being movable more easily and rapidly at less cost of relocation) and improved environment resulting in improved moral and productivity of the employees. In a typical approach to the open plan office, the "landscaping" is accomplished with individual pieces of functional, easily movable furniture and movable acoustical privacy screens.
Properly planned open office landscaping yields an office area which is functional and visually open while providing the acoustical privacy required by the employees to accomplish their tasks comfortably and efficiently. Five major components contribute to the necessary acoustical balance. These components are: carpet, masking sound, divider screens, ceiling and walls. The primary function of carpeting on the floors is to reduce traffic noise, rather than to absorb sound. It is common practice to provide an electronically generated masking sound emanating from speakers above the ceiling. The purpose of the masking sound is to interfere with speach intelligibility across the divider screens. The sound itself is virtually undetectable, but is ever present in the total environment.
Divider screens constitute an essential part of the open office landscaping, filling the dual role of giving a degree of visual privacy, as well as absorbing sound and preventing its transmittance through to the next work area. The typical divider screen is about 5 and 1/2 feet wide, 4 and 1/2 high, double sided and goes close to the floor, being supported by protruding feet or the like.
The ceiling is of major importance since sound can be reflected by it at an angle and thus travel from one work area to another. The usual approach is to apply sound absorbing panels to the ceiling or to suspend such panels by mechanical means.
In almost all open plan offices, the walls require acoustic treatment. As a general rule, walls less than 65 feet apart require treatment to prevent sound reflection. Those further apart still require acoustic treatment for those people located adjacent the walls. Prior art workers have generally taken two approaches toward the acoustic treatment of walls. One is the use of carpet which, while decorative and relatively inexpensive, is not a very effective sound absorber. The other approach is to use acoustical wall panels. There are many sound absorbing materials currently available for architectural applications, such as glass batts, mineral boards, etc. some provided with facings of vinyl, woven glass fibers or the like. While prior art panels are often effective sound attenuators, they are frequently characterized by one or more problems such as rigidity (being nonconformable to preexisting irregular surfaces and coming in predetermined sizes), difficult to maintain, repair or seam, and the like. Exemplary sound attenuating panels are taught, in U.S. Pat. Nos. 4,056,161 and 4,077,491. Exemplary rigid panels are taught in U.S. Pat. Nos. 3,148,693; 3,265,154; 3,583,522 and 4,111,081. A flexible sound attenuating material is taught in U.S. Pat. No. 3,253,947. U.S. Pat. Nos. 3,448,823 and 3,919,444 teach acoustical panels having an outer surface of woven glass fibers.
The two most important properties of an acoustical laminate are good sound absorption and excellent flame retardance. Sound absorption is a measure of how much sound energy impinging upon an object is absorbed by the object and how much is reflected back at different frequencies. A standard test for sound absorption is the ASTM C-423-77, Reverberation Room Method. The sound absorption value of a given material is expressed as N.R.C. (the Noise Reduction Coefficient). The N.R.C. is an arithmetic average of test values measured at 250, 500, 1,000 and 2,000 cps, to the nearest 0.05. Products currently available have a sound absorption value of 0.40 or better. Typically, for example, divider screens have an N.R.C. value of about 0.85. An acceptable sound absorbing wall covering or wall panel should have an N.R.C. value of at least from 0.40 to about 0.85. The major frequencies that are of concern in office areas are the 2,000-4,000 hertz band (speech range), in which range the N.R.C. of a good acoustical wall covering or wall panel should be at least about 0.80.
Flame retardance is extremely important in buildings, especially on vertical surfaces. The regulations vary from state-to-state and city-to-city. The most frequently specified test is the ASTM E-84-74 Tunnel Test. In this test a material is rated according to flame propagation, in Classes A (0-25), B (26-75), C (76-200) and D (201-). It is generally assumed that an acoustical wall covering should have a Class A rating to qualify for most applications.
The acoustical laminates of the present invention demonstrate excellent acoustical properties, achieving a N.R.C. value in excess of 0.80 in the range of 2,000 to 4,000 cps. While, as a general rule, composite acoustical materials usually demonstrate acoustical properties equal or worse than the acoustical properties of their individual parts, the laminates of the present invention demonstrate an unexpected synergism in that the acoustical properties of the laminates are considerably improved over the acoustical properties of the facing and the backing layers when tested alone. The non-wooven, needle punched, inherently non-flamable fibers (such as glass or mineral fibers) of the facing material yield very low smoke generation with the proper finish, are non-melting (resistant to cigarette burns and the like) and protect the foam or fiber mat backing so that the laminates achieve a flame retardant rating of A.
The non-woven, needle punched facing presents excellent aesthetic properties (look, texture, feel and the like). The facing material has a textile appearance and can be given a three dimensional surface (ribbed, quilted, etc.). The facing can be appropriately colored and imprinted or screenprinted with a design.
The laminates of the present invention can be readily cut or trimmed and since the facing is of non-woven, needle punched glass or mineral fibers or the like, there is less tendency for the edges of the facing to fray than with woven materials. This, together with the fact that the facing has a nonuniform geometry, due to inherent random fiber placement and needle marks, results in the ability of the laminates of the present invention to be easily seamed with low visibility seams to achieve a monolithic wall appearance and to be easily repaired.
The non-woven needle punched fiber facing is characterized by excellent abrasion resistance. As a result, the laminates of the present invention are resistant to being rubbed and demonstrate excellent maintenance and cleanability characteristics without change of appearance. The laminates will hold thumb tacks and the like.
The laminates of the present invention are supplied as flexible wall coverings, provided in roll form. As a result, the laminates have an ability to conform to irregular surfaces and to make tight radius bends. In fact, they can be used as portable sound absorbent screens which can be deployed or rolled up, as needed. They are characterized by ease of handling and application or installation with conventional tools. Because of their flexible form, they can be applied to an existing surface with wall paper paste or the like, or attached to an existing surface by means of a pressure sensitive adhesive applied to the rear surface of the laminates.
Finally, the acoustical laminates of the present invention can have their sound absorption efficiently increased by the addition of high surface area fillers in the facing layer.